We propose to elucidate the structure and function of a family of GTP-binding proteins that transduce hormonal and other regulatory signals across cell membranes. This family includes three known members: Transducin, which couples photorhodopsin to stimulation of a cyclic GMP phosphodiesterase in vertebrate retina; Ns, which couples hormone receptors to stimulation of adenylate cyclase; Ni, which couples other hormone receptors to inhibition of adenylate cyclase. The project involves molecular clongin and sequencing of the genes that encode the Alpha and Beta subunits of these three homologous proteins. The cloned sequences will allow us to investigate the following questions: 1. What are the mutations (changes in base sequence) that produce altered functions of the Alpha subunit of Ns in S49 lymphoma mutants with phenotypic defects in regulation of adenylate cyclase? 2. What changes in base sequence produce the generalized decrease in Ns activity in cells of patients with an inherited disorder of hormones and other stimuli alter expression of Ns and Ni in tissue culture models of cell differentiation? 4. How are differences in structure (amino acid sequence deduced from base sequence) among transducin, Ns, and Ni related to their different functions? 5. Can mutations whose penotypes have already been defined (in S49 cells and pseudohypoparathyroisism), shed light on the relation between structure and function of the coupling proteins? 6. Can the relation between structure and function of thes proteins be elucidated by producing (in vitro) defined mutations in genes that encode their subunits and expressing the mutant genes in appropriate recipient cells? Achievement of the goals of this project will elucidate basic mechanisms of hormone action and signal transducton in vertebrate organisms and define the molecular basis of an inherited human disease.